EXOSAT observations of the Seyfert galaxy NGC 7469; rapid hard X-rayvariability and a soft X-ray excess.

Abstract

The results of a series of EXOSAT observations of the Seyfert 1 (and starburst) galaxy NGC 7469 performed in July 1984 are presented. During one observation, hard X-ray variability by a factor 2 within 5 hr was found, while the soft X-ray intensity remained constant. In addition the spectral data indicate an excess of soft X-ray emission over that expected from extrapolation of the hard X-ray continuum. There is no evidence for any variability of this soft excess. An extranuclear origin associated with the starburst region seems unlikely, as is soft X-ray emission from any hot confining intercloud medium in the Seyfert narrow-line and broad-line regions, due to the high (greater than 5 x 10 to the 43rd erg/s) luminosity involved in this soft excess. However, soft X-ray emission from a hot optically thin wind cannot be excluded. An alternative is an extra soft X-ray component from the compact nucleus itself.